 FRET
 To prove that we can obtain a “Key” with a proper affinity to its antibody, we use 
 tumor antigen p185her2/neu ECD and the scFv of its antibody chA21 as an example. In 
the “Protein Engineering” part, we discussed how we had designed the 8 mutants of 
p185her2/neu ECD. To find out whether the affinity between chA21 scFv and these 
mutants are proper or not, we design a series of experiments based on “Fluorescence 
Resonance Energy Transfer (FRET)”.
 Forster resonance energy transfer (FRET) is a process by which a fluorophore (the 
 donor) in an excited state transfers its energy to a neighboring molecule (the acceptor) 
 by nonradiative dipole-dipole interaction [1, 2]. The efficiency of this energy transfer is 
 inversely proportional to the sixth power of the distance between donor and acceptor, 
 making FRET extremely sensitive to small changes in distance [3], and FRET is thus a 
 very efficient way of detecting protein-protein interaction.